This invention relates to a muffler for internal combustion engines or the like.
Various types of mufflers are known in the art, such as damper baffle type mufflers, resonance box mufflers, etc. In acoustic theory, there is also known a device called Koenig trombone which is normally used in laboratories or schools to carry out experiments on sound waves. A koenig trombone, as shown in FIG. 1, includes a bent stationary pipe 1 having two ports 2 and 3; a second bent pipe 4 can slide on the first one. In front of one of the ports, a tuning fork 5 is vibrated and the sound is listened at the other port while slowly sliding the movable pipe. Depending upon the positions of this movable pipe, maximum and minimum level sounds can be heard. Minimum level sounds occur when waves, having passed along pipe 1 and pipe 4 respectively, reach the port 3 in phase opposition, i.e. the path in the pipe 4 is the same as that in the pipe 1 plus a distance equal to an odd integer multiple of the half-wavelength of the sound wave coming from the tuning fork 5. So, when single frequency waves are in a phase opposition condition, a substantially full cancelling of the sound at the outlet of the device is obtained.